On 5/4/10 4:25 PM, Timothy W. Hilton wrote: > Hi Jeff, > > Thanks very much for your response. As you noted, I do not understand > the Basemap global sinusoidal coordinate system. Does this statement > not set up a global sinusoidal cartesian coordinate system centered at > (lon = 0.0, lat = 0.0)? >
Tim: It's a global sinusoidal projection, but x=0,y=0 is not at lon_0,lat_0. >> from mpl_toolkits.basemap import Basemap >> m = Basemap(projection='sinu', resolution=None, lon_0=0.0, lat_0=0.0) >> print m(0,0,inverse=True) (-176.20919036912957, -89.999999999808395) I forget why I did it this way, but I think it has to do with the fact that the matplotlib coordinate system has 0,0 in the lower left corner, not the middle. At any rate, apply a offset to x and y to map to your global coordinate system. -Jeff > m = Basemap(projection='sinu', resolution=None, lon_0=0.0, lat_0=0.0) > > If so, I would expect m(0.0, 0.0) to return (0.0, 0.0) and m(0.0, 0.0, > inverse=True) to return (0.0, 0.0). Instead, I get: > >>>> m(0.0,0.0) >>>> > (20015077.371199999, 10007538.6856) > >>>> m(0.0,0.0,inverse=True) >>>> > (-176.20919036912957, -89.999999999808395) > > Sorry if I am being obtuse. Many thanks for your help. > > -Tim > > On Tue, May 2010, 04 at 04:01:21PM -0600, Jeff Whitaker wrote: > >> On 5/4/10 2:03 PM, Timothy W. Hilton wrote: >> >>> Hello matplotlib users, >>> >>> I am having trouble understanding the coordinate transformations in >>> Basemap and pyproj. I have gridded MODIS vegetation data, with upper >>> left corner and lower right corner given in projection coordinates >>> (meters). I want to contour the data with Basemap. The data are in a >>> sinusoidal projection, but the coordinates do not correspond to what >>> Basemap seems to expect. >>> >>> The code below illustrates the problem. Proj translates the upper >>> left to lat/lon correctly (-92.327237416031437, 30.141972433747089), >>> while Basemap does not. >>> >>> #-------- code -------- >>> >> >from mpl_toolkits.basemap import Basemap >> >from mpl_toolkits.basemap import pyproj >> >>> ulm = [-8895604.1573329996, 3335851.5589999999] #upper left, meters >>> lrm = [-7783653.6376670003, 2223901.0393329998] #lower right, meters >>> >>> sinu = pyproj.Proj(proj='sinu', lon_0=0.0, x_0=0.0, y_0=0.0) >>> m = Basemap(projection='sinu', resolution=None, lon_0=0.0) >>> >>> print "ULM: " + str(ulm) >>> print "Proj: " + str(sinu(ulm[0], ulm[1], inverse=True)) >>> print "Basemap: " + str(m(ulm[0], ulm[1], inverse=True)) >>> #----- end code -------- >>> >>> This gives: >>> ULM: [-8895604.1573329996, 3335851.5589999999] >>> Proj: (-92.327237416031437, 30.141972433747089) >>> Basemap: (-159.99950210056144, -59.99995206181125) >>> >>> I'm sure I'm missing something really simple, but I've read a lot of >>> documentation and I'm not sure what. >>> >>> Many thanks for any help. >>> >>> Best, >>> Tim >>> >> Tim: Basemap is using pyproj under the hood, but only supports a >> subset of possible proj4 projections. The basemap sinusoidal >> projection is global - you can't specify a subregion of the globe. >> I think that's where the discrepancy is coming from. I'm sure >> there's a way to plot your MODIS data on a global sinusoidal >> projection - but it will involve transforming the coordinates to the >> Basemap global sinuosidal coordinate system. >> >> -Jeff >> >> -- Jeffrey S. Whitaker Phone : (303)497-6313 Meteorologist FAX : (303)497-6449 NOAA/OAR/PSD R/PSD1 Email : jeffrey.s.whita...@noaa.gov 325 Broadway Office : Skaggs Research Cntr 1D-113 Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
